(a) Field of the Invention
The present invention relates to a negative active material for a rechargeable lithium battery, a method of preparing the same, and a rechargeable lithium battery including the same.
(b) Description of the Related Art
A rechargeable lithium battery has recently drawn attention as a power source for small portable electronic devices. It uses an organic electrolyte and thereby has twice the discharge voltage of a conventional battery using an alkali aqueous solution, and accordingly has high energy density.
For a positive active material of a rechargeable lithium battery, lithium-transition element composite oxides being capable of intercalating lithium, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1−xCoxO2 (0<x<1), LiMnO2, and so on, have been researched.
For a negative active material of a rechargeable lithium battery, various carbon-based materials such as artificial graphite, natural graphite, and hard carbon have been used, which can all intercalate and deintercalate lithium ions. Graphite of the carbon-based material increases discharge voltage and energy density for a battery because it has a low discharge potential of −0.2V compared to lithium. A battery using graphite as a negative active material has a high average discharge potential of 3.6V and excellent energy density. Furthermore, graphite is most comprehensively used among the aforementioned carbon-based materials since graphite guarantees a better cycle life for a battery due to its outstanding reversibility. However, a graphite active material has a low density and consequently a low capacity in terms of energy density per unit volume when using the graphite as a negative active material. Further, there are some dangers, such as explosion or combustion, when a battery is misused, overcharged, or the like, because graphite is likely to react with an organic electrolyte at a high discharge voltage.
In order to solve these problems, a great deal of research on an oxide negative electrode has recently been performed. For example, amorphous tin oxide developed by Japan Fuji Film Co., Ltd. has a high capacity per weight (800 mAh/g). However, this oxide has resulted in some critical defects such as a high initial irreversible capacity of up to 50%. Furthermore, part of the tin oxide has tended to be reduced into tin during the charge or discharge reaction, which is a disadvantage for use in a battery.
Referring to another oxide negative electrode, a negative active material of LiaMgbVOc (0.05≦a≦3, 0.12≦b≦2, 2≦2c−a−2b≦5) is disclosed in Japanese Patent Publication No. 2002-216753. The characteristics of a lithium secondary battery including Li1.1V0.9O2 were also presented in the 2002 Japanese Battery Conference (Preview No. 3B05).
However, such an oxide negative electrode does not show sufficient battery performance and therefore there has been a great deal of further research into oxide negative materials.